Luminaires employing elongated fluorescent lamps designed to direct lamp rays broadly and upwardly toward a target surface (e.g. ceiling), thereby achieving general illumination by reflection of said light rays from said target surface (ceiling), are well known in the industry. Similarly known are luminaires that are positioned adjacent to vertical surfaces in a manner that directs light output upwardly toward, e.g., a ceiling, and broadly away from the vertical surface/wall. Such luminaires may contain multiple elongated lamps aligned in tandem within a single elongated housing.
It is equally well known that elongated fluorescent lamps produce less light output (radiant exitance) in cathode regions located at the ends of the lamp as compared to light output at a central region of the lamp, i.e. the area between the cathode regions. Each cathode region is generally defined as an area around the lamp's internal electrodes. In some cases, the region of diminished output at the cathode region may be approximately 1½″ to 2″ in length. In addition, these elongated fluorescent lamps have an opaque closure cap on each end that is generally ½″ in length from which no light is emitted. In elongated luminaires where tandem lamping is used, the occurrence of back-to-back lampholder brackets and lampholders, combined with the adjacent lamp caps and low-output cathode regions of the lamps, results in an extended region of diminished radiant exitance at a central point along the length of the luminaire (in the case where two similar sized lamps are used). This area of diminished output has little or no effect upon the distribution of luminance on a surface or area distant from the luminaire. However, this condition invariably results in a noticeable reduction in surface luminance (hereinafter sometimes referred to as, “socket shadow”) on any surface proximate to the lamps. It is generally desirable and advantageous to eliminate occurrences of socket shadow.
Since luminaires such as those discussed above generally employ an opaque or perforated backlight shield to manage/modify the direct illumination of a vertical surface occurring adjacent to the luminaire along the major portion of the lamp(s), it is common to reduce the width of the back light shield or eliminate the shield near the ends of each lamp in an effort to reduce occurrences of socket shadow between adjacent tandem mounted luminaires. However, this practice does not fully eliminate socket shadow and additional reduction is desirable. Accordingly, it is desirable and advantageous to provide a device for achieving greater reduction of socket shadow on the vertical surface proximate to a tandem lamp luminaire which does not substantially degrade a desired light output of the luminaire.